Sound

Sound

1. Analogue

   • Music and speech vary continuously in frequency and amplitude. In the same way, analogue signals can vary in frequency, amplitude or both. The diagram shows a typical oscilloscope trace of an analogue signal which varies in the same way as the sound signal it represents.

2. Digital

   • Digital signals are a series of pulses consisting of just two states, ON (1) or OFF (0). There are no values in between. The sound is converted into a digital code of 0s and 1s, and this coded information controls the short bursts of waves produced by a source. DAB radio is Digital Audio Broadcast radio – it is transmitted as digital signals. The diagram shows a typical oscilloscope trace of a digital signal.

3. Sample Rate

   • Only in digital. Take snapshots at intervals. Number in a second defines the rate. Higher rate means higher quality sound. Higher rate means bigger file size
   • Measured in Hertz or Hz/kHz

4. Sample resolution

   • The number of different values available to take on. The more the better. More values mean larger file size.

5. Calculating file size

   • Mono sound
     • sample rate x sample resolution x seconds = bits
   • Stereo sound
     • sample rate x sample resolution x seconds x 2 = bits

6. Bitrate

   • The amount of information outputed per second. Usually kbps.
   • bitrate = bits per sample x sample per second x number of channels

7. filesize = (bitrate x duration) / 8